The invention relates to an anti-jackknifing device with a friction brake for an articulated motor vehicle, where one of the braked elements of the friction brake is connected to the front vehicle, the other one to the trailer, and it has brake-actuating control unit which controls the brake by influencing the selected run-dynamic characteristic of the motor vehicle.
Several devices are known for preventing the articulated motor vehicle from abnormal jackknifing, in which the anti-jackknifing torque is produced by a friction brake system around the articulation connecting the two vehicles.
In the device described in the U.S. Pat. No. 4,109,929, a brake disc is fixed on the trailer and the surrounding brake bracket carrying the friction linings is guided in the slot of the coupling of the semi-trailer tractor. The brake system is hydraulically operated, controlled with the control unit influenced with the differential pressure prevailing in the double actuation space of the hydraulic power-assisted steering unit. When the articulated vehicle travels straight line same liquid pressre prevails in the actuating spaces of the power-assisted steering unit, and since there is no differential pressure, the control unit does nor receive an influencing signal, consequently the brake actuating cylinder is kept by the control unit in constant connection with the source of the pressure medium and the friction brake is in the braked condition. When the vehicle travels straight, the device produces an advantageous effect against lateral deviations of the trailer, but in a curve it produces reduced torque against the jackknifing angle variation in order to allow the turn of the articulated motor vehicle, as a result of which it produces insufficient pressure in the curve against the abnormal jackknifing angle variation. Increasing torque is produced by the device in the curve only when the driver steers the front wheels towards the mid-position of the steering mechanism, i.e. when the driver corrects the arc of travel.
Also known are such frictional anti-jackknifing devices, where the torque produced by the brake against the jackknifing angle variation depends on the extent of the jackknifing angle, irrespective of the angle of the steered wheel.
In another known solution, the friction brake producing the torque against the jackknifing angle variation is interconnected and synchronized with the air brake system braking the wheels of the motor vehicle.